Document: TAN-3-69-27

The effects of fire frequency on initial successional patterns in Yellowstone National Park.

SCHOENNAGEL, T.* ¹, M.G.TURNER ¹ and W.H.ROMME ²

University of Wisconsin, Madison, WI 53706, USA ¹
Fort Lewis College, Durango, CO, USA ²

Abstract:
Climate change is expected to alter the frequency of disturbances such as fire, resulting in significant changes in vegetation patterns and carbon sequestration across forested landscapes. The objective of our research is to test for and predict qualitative shifts in successional pathways (e.g. conversion from forest to non-forest, or from dense to sparse stands) and understory community composition in response to varying fire intervals and levels of serotiny across the subalpine plateaus of Yellowstone National Park. Serotiny is a variable trait across the Yellowstone landscape, exhibited only by some individuals of inland lodgepole pine (Pinus contorta var. latifolia), which produce mature closed cones later in life that open only when heated by fire, resulting in high-density seedling establishment. The age of closed cone production is pivotal in predicting the effects of fire frequency on lodgepole pine seedling densities, but is not well documented. By coring trees from different stand-replacing fire dates, we found that initial production of serotinous cones occurs between 24 and 37 years of age. This suggests that significant threshold responses to fire frequency may be present in areas where the percentage of serotinous individuals is high, whereby fire intervals less than 24 years produce low seedling densities, and fire interval greater than 40 years produce high seedling densities. We also sampled a range of stand-replacing fire intervals in areas with low stand-level proportion of serotinous individuals. With all sites burned in 1988 and a previous time, we were able to compare the effects of fire interval on postfire lodgepole pine seedling densities and understory cover and composition. Our results show that although some understory species exhibited sensitivity to fire frequency, overall biotic cover showed no significant differences. Short-interval fires (~10 yrs), however, resulted in fewer lodgepole pine seedlings compared to longer fire intervals (~50 yrs; p = 0.001). In addition to the effects of fire severity and fire size, these results indicate that fire frequencies may also alter initial pathways of succession across the Yellowstone landscape, with most dramatic shifts expected as a function of interaction with stand-level proportion of serotiny.

Keywords: disturbance, succession, fire ecology, global climate change

This abstract is being presented at: 10:30 AM in session:
Poster Session #12: Disturbance Ecology.